Infusion devices may be used to deliver an infusion media (e.g. a medication such as insulin) to a patient. Such devices may be designed to be implanted into a patient's body to deliver predetermined dosages of the infusion media to a particular location within the patient's body, e.g. in the venous system, the spinal column, or within the peritoneal cavity. A known infusion device of the type described above includes a drive mechanism that includes a reciprocating pumping element, otherwise known as an actuator member. The reciprocating pumping element includes an actuator that has a piston portion coupled to an armature portion, also known as a piston actuator or pole. The piston portion is configured to reciprocate within a piston channel when a solenoid coil is alternately energized and de-energized. That is, when the solenoid is energized, magnetic flux causes the actuator to move very quickly (i.e. in the order of 2-3 milliseconds) until it reaches a stop member. This corresponds to the pump's forward stroke and results in the delivery of a predetermined dosage of infusion media from an outlet chamber to the patient. When the solenoid is de-energized, the lack of magnetic flux allows the actuator to return to its original position under the force of a spring or other return mechanism. This, in turn, causes the pressure in the piston chamber to fall. The reduced pressure in the piston chamber causes infusion media to flow from a reservoir through an annulus between the actuator piston and the piston cylinder wall to refill the piston chamber, thus equalizing the pressure between the reservoir and the piston chamber and preparing the pump for its next pumping or delivery stroke. This is referred to as the refill stroke. The annulus between the actuator piston and the piston cylinder may be very small (i.e. in the order of 150 to 250 microinches radially), resulting in an outlet chamber refill process that takes between about 1 to 2 seconds. In contrast, the pump's forward (delivery) stroke may be approximately 500 times faster than the refill process.
Over time, the motion of the piston back and forth may result in wear. Furthermore, uneven loads may have a tendency to tip the piston to one side of the cylinder or the other. Tipping of the piston may continuously wear a single location on the piston or cylinder, resulting in not-insignificant long term damage. Modifications to the piston, cylinder, and other corresponding pieces of a drug pump that reduce this wear are therefore continuously desired.